The present invention relates to a polyimide film having improved adhesion prepared by coating the surface of a partially cured or partially dried polyamide acid film with a solution of a specified metal salt and then heating the coated film to imidize the polyamide acid to the polyimide as well as to dry the film.
Polyimide film is well-known for its outstanding properties such as heat resistance, low temperature resistance, chemical resistance, electrical insulation and mechanical strength. Such polyimide film is widely used as an electrical insulating film and as a base for flexible printed circuits. In such applications, the polyimide film is usually bonded to a copper foil with an acrylic or epoxy adhesive and, therefore, good adhesion is an important property requirement.
U.S. Pat. No. 4,742,099, issued to Nagano et al., on May 3, 1988, discloses a polyimide film containing from 30 to 800 ppm of a titanium-based organometallic compound for improving adhesion. The polyimide film of the invention does not contain an organometallic titanium compound.
U.S. Pat. No. 3,389,111, issued to McKeown et al., on Jun. 18, 1968, discloses polyimide films having improved corona resistance containing organo-metallic compounds of Groups IVb and Vb of the Periodic Table. The polyimide film of the invention does not contain Group IVb or Vb organometallic compounds.
U.S. Pat. No. 4,797,307, issued to Kunimoto et al., on Jan. 10, 1989, discloses a polyimide film having improved adhesiveness prepared by coating the surface of the film with a heat-resistant aminosilane, epoxysilane or titanate treating agent. The polyimide film of this invention is not coated with an aminosilane, epoxysilane or titanate treating agent.
An object of the present invention is to provide a polyimide film which has improved surface adhesiveness.
More particularly, the invention provides a polyimide film which has improved surface adhesion when bonded to metal foils, such as copper foil, by means of an epoxy, acrylic or other heat-resistant resin adhesive.